The present invention relates to a scraper blade for use, in particular, as a conveyor belt scraper.
SE-B-468390, and the corresponding U.S. Pat. No. 5,197,587, disclose a scraper blade adapted to be used in a conveyor belt scraping device. The scraper is made of a homogeneous elastomeric or plastic material and provided with an inner stiffening member in the form of a piece of sheet-metal which is inserted into a groove in the scraper. The abrasion resistance of this type of homogeneous scraper has proven to be insufficient for certain applications.
A similar scraper is disclosed in EP-A-0893376. This scraper has an inner stiffening member equivalent to the removable stiffening member of the scraper according to the above-mentioned specification. In other ways, the scraper is similar, i.e. the active scraper tip is made of a homogeneous material. Consequently, nor is this scraper optimal for said applications.
EP-A-0573688 also discloses a conveyor belt scraper having a tip which is made of a homogeneous material and which, during use, is subject to substantial abrasive wear and, therefore, is removably mounted.
Various proposals to increase the abrasion resistance have been put forward. Some of these are disclosed in U.S. Pat. No. 6,082,524, EP-A-0566486 and U.S. Pat. No. 5,692,595, where the tip of the scraper has been provided with an inset of cemented carbide. However, this solution causes unnecessary wear on the surface scraped by the scraper.
GB-A-1454763 discloses a scraper blade which is made of a two-layer laminate, in which one layer is made of an elastomeric material of a softer quality to achieve efficient scraping and the other layer is of a harder quality to form a support for the softer layer. In use, the scraper blade can be mounted in such manner that the harder layer is facing forward or that the softer layer is facing forward. The latter mounting is preferred when the scraper is used for scraping wet materials. In the embodiment shown, the scraper blade is arranged perpendicularly to the surface to be scraped. If the scraper is used as a prescraper to scrape an arched surface and, therefore, the scraper blade is applied obliquely against this surface, there is a considerable risk of the layer of soft material forming a thin lip, which does not come off and thus has a detrimental effect on the scraping result.
The latter problem has been observed in U.S. Pat. No. 4,658,949, which provides another way of maintaining an essentially constant scraper tip, i.e. of preventing the outer end of the pointed scraper from bending outwards from the scraped surface, which would otherwise lead to a complete or partial loss of scraping ability. This prior-art technique is based on the idea that the outside of the scraper is provided with fracture lines in the form of section lines or thin slits, which extend a considerable distance into the scraper from its outside so that the tip, after being worn to a given depth, simply breaks off, thus revealing a new efficient scraper tip portion. One disadvantage of this prior-art construction is that the fracture lines weaken the scraper and give the new tip a blunt shape.
An object of the present invention is to provide a new scraper blade, which has both a longer useful life and better scraping effect than the above-mentioned scraper blades according to prior art. Another object of the invention is to provide a scraper blade which, owing to its construction, maintains its scraping effect better and maintains the shape of the efficient scraper tip.
To summarize, the invention relates to a scraper blade which has at one end a scraper tip and at the other end a mounting base. The scraper tip is outwardly tapered. The scraper blade has at least two layers of different materials. In the invention, the layer of material adapted to form the actual scraper tip is made of a material that is both softer and more abrasion resistant than said at least one other layer. If the scraper blade has only two layers, the softer and more abrasion resistant layer will be facing forward, i.e. it will be the first to meet the surface to be scraped.
The characteristics of the invention are defined in the independent claim. The dependent claims define particularly preferred embodiments of the invention.
As mentioned above, the technique consisting in using a scraper with two layers of different hardness is already known from GB-A-1454763 in connection with scraping wet surfaces. In this case, two layers of material are used, one having a hardness of 75-98xc2x0 Shore A and the other having a hardness of 65-88xc2x0 Shore A. In the specification, it is stated that the scraper can be operated in both directions, i.e. either with the softer or with the harder layer of material first. This indicates that materials with similar or substantially similar abrasion resistance are used to obtain an even wear on both layers, which are arranged essentially perpendicularly to the scraped surface.
In the present invention, however, the harder material shall have a lower abrasion resistance in order to be worn faster and thus to permanently maintain a flexible scraper lip of a softer material in contact with the scraped surface.